Historically, synthetic fibers for use in apparel, including polyester fibers, have generally been supplied to the textile industry for use in fabrics and garments with the object of more or less duplicating and/or improving on natural fibers. For many years, commercial synthetic textile filaments, such as were made and used for apparel, were mostly of deniers per filament (dpf) in a similar range to those of the commoner natural fibers; i.e., cotton and wool. More recently, however, polyester filaments have been available commercially in a range of dpf similar to that of natural silk, i.e. of the order of 1 dpf, and even in subdeniers, i.e., less than about 1 dpf, despite the increased cost. Various reasons have been given for the recent commercial interest in such fine filaments, such as of about 1 dpf, or even subdeniers.
Much has been written recently about this increasing interest in fine denier polyester filaments. Very little technical detail has, however, been published about any difficulties in spinning (i.e., extrusion and winding) techniques that have been used, or even would be desirable, for manufacturing such fine filaments, although it has been well understood by those skilled in the art that conventional preparation and handling techniques could not be used for such fine filaments. For instance, in Textile Month, June 1990, pages 40-46, three approaches are discussed for making microfibers; namely, 1) conventional spinning to fine deniers, 2) splitting bicomponent fibers (of higher deniers), and 3) dissolving away a component from bicomponent fibers of higher denier. It will be understood that the 2nd and 3rd approaches involve bicomponent spinning to form filaments first of higher denier, and processing such spun higher denier filaments to obtain the filaments of reduced denier; such processing techniques are not the subject of the present invention.
The present invention is concerned with the preparation of fine filaments by a novel direct spinning/winding process, in contrast with a process of first spinning and winding up bicomponent filaments of higher denier which then must be further processed to obtain the reduced fine denier filaments that are desired for use in textiles. Another 2-stage possibility of manufacturing filaments of reduced denier is to spin filaments of greater than one denier, and then, draw the filaments after the spinning operation, but this possibility has important disadvantages that have been discussed in the art; on the one hand, there are practical limitations to the amount of draw that can be effected; there are also product disadvantages in the properties of drawn yarns, as contrasted with direct spin-oriented yarns; and the cost of such processing (i.e., drawing) has to be considered, especially when the drawing is performed as a separate operation, after first packaging the spun filaments, such as single yarn or warp drawing. Such drawing proposals may have involved conventional drawing techniques, or may have involved other techniques, e.g., aerodynamic effects or reheating the filaments after they have been solidified, but still advancing under sufficient tension to draw (sometimes referred to as space-drawing, if performed without godets of differential speeds). Some direct spinning processes that have been proposed have relied on use of specific polymer compositions, for instance specific viscosities, that have disadvantages, so it would be desirable to use a process that does not require use of special viscosities or other special compositional aspects.
To summarize, previous polyester filament manufacturing techniques that have been disclosed in the art have not been specifically directed to and have not been suitable in practice for producing fine denier polyester filaments by a simple direct spinning/winding operation, or have involved limitations and disadvantages. So it has been desirable to provide such a direct spinning process for manufacturing fine polyester filaments of the desired dpf and properties without such disadvantages. The present invention solves this problem. The filaments of the invention are "spin-oriented", the significance of which is discussed hereinafter.